Provided is a novel hydrogen separation membrane formed of a Nb—W—Mo-based alloy. A method for separating hydrogen using the hydrogen separation membrane and hydrogen separation conditions are selected by a particular procedure. A hydrogen separation membrane formed of the Nb—W—Mo-based alloy membrane. A method for separating hydrogen using the Nb—W—Mo-based alloy membrane and the conditions for separating hydrogen using the Nb —W—Mo-based alloy membrane are set by measuring the hydrogen pressure P of a hydrogen atmosphere for the Nb—W—Mo-based alloy membrane and the dissolved hydrogen content C of the Nb—W—Mo-based alloy membrane at a temperature T; generating a PCT curve associating the temperature T, the hydrogen pressure P, and the dissolved hydrogen content C on the basis of actual measurement data about the three requirements; and setting operating temperature and primary and secondary hydrogen pressure conditions by determining the relationship between the dissolved hydrogen content C and the brittle fracture of the Nb—W—Mo-based alloy membrane on the basis of the PCT curve to evaluate critical dissolved hydrogen content related to hydrogen embrittlement resistance.